Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Measurement of charged-particle event shape variables in inclusive root(s)=7 TeV proton-proton interactions with the ATLAS detector

The measurement of charged-particle event shape variables is presented in inclusive inelastic pp collisions at a center-of-mass energy of 7 TeV using the ATLAS detector at the LHC. The observables studied are the transverse thrust, thrust minor, and transverse sphericity, each defined using the final-state charged particles' momentum components perpendicular to the beam direction. Events with at least six charged particles are selected by a minimum-bias trigger. In addition to the differential distributions, the evolution of each event shape variable as a function of the leading charged-particle transverse momentum, charged-particle multiplicity, and summed transverse momentum is presented. Predictions from several Monte Carlo models show significant deviations from data

Molecular cryosorption properties of porous copper, anodised aluminium and charcoal at temperatures between 10 and 20 K

There exist several theorems which state that when a matroid is representable over distinct fields F1,...,Fk , it is also representable over other fields. We prove a theorem, the Lift Theorem, that implies many of these results. First, parts of Whittle's characterization of representations of ternary matroids follow from our theorem. Second, we prove the following theorem by Vertigan: if a matroid is representable over both GF(4) and GF(5), then it is representable over the real numbers by a matrix such that the absolute value of the determinant of every nonsingular square submatrix is a power of the golden ratio. Third, we give a characterization of the 3-connected matroids having at least two inequivalent representations over GF(5). We show that these are representable over the complex numbers. Additionally we provide an algebraic construction that, for any set of fields F1,...,Fk , gives the best possible result that can be proven using the Lift Theorem

Strong pinning in melt-textured YBa2Cu3O7-delta with non superconducting Y2BaCuO5 inclusions.

We report on a detailed study of the temperature and field dependence of the critical current density J(C) (T, H) in the temperature range 5 K - 100 K and fields up to 50 tesla, in high quality melt-textured YBa2Cu3O7 with 20wt% Y2BaCuO5, fabricated by Directional Solidification. From magnetic measurements, J(C) was determined as approximate to 10(6) A/cm(2) at H = 1 tesla and T = 5 K. From the normalised relaxation rate S (T, H) and the pinning potential U (J, H), determined from detailed SQUID measurements, different pinning regimes have been identified, in accordance with 3D collective pinning theory. The kink on U (J, H) and S (T, H) can be described as a transition from a small bundle to a big bundle collective pinning regime. Furthermore, the J(C) (T, H) dependence has been investigated using high pulsed magnetic fields of up to 50 Tesla The estimated irreversibility fields show the potential of these materials for high field applications